GB1473969A - Recessed screw heads and drivers - Google Patents

Abstract

1473969 Forging; screwdrivers PHILLIPS SCREW CO 10 Sept 1975 [12 Sept 1974] 37236/75 Headings B3H and B3N [Also in Division F2] To improve the grip between a screwdriver and the driver-engageable surfaces of a screw head, a small rib, a few thousandths of an inch thick, is formed on at least one screw-engaging surface of the screwdriver. Preferably the driver engageable surfaces of the screw have similar but differently orientated ribs (see Division F2) into which the screwdriver ribs can bite, since the screw is normally of softer material that the driver. In Fig. 11, each driving surface 46 of a cruciform bit has two transverse ribs 50, 50a. Similar ribs may also be formed on the back-out faces 46<SP>1</SP> (Fig. 16, not shown). In Fig. 16A, a rib 52 extends along the free edge of each driving face, and optionally also of each back-out face, the rib being a projection, Fig. 17, or formed by hollowing the blade at 5A, Fig. 17A. A second rib (52a) may be provided parallel to the rib 52 (Fig. 19, not shown) or at an angle to the rib 52, (54) (Fig. 21, not shown). In Fig. 27, a series of transverse ribs 60 is provided on the inclined free edge 56 of each blade 34 of a cruciform bit. In Fig. 28 a rib 64 is formed at the bottom edge of each intermediate surface 36 separating the blades 34 of a cruciform bit, and a second rib (64a) (Fig. 33, not shown) may be added part-way up each surface 36. Similar ribs may be provided on the blades of a three blade bit (Figs 51-55, not shown). A punch 150, Figs 58, 59, for cold-forming the driving recess of a screw head has shallow grooves 168, e.g. a few thousandths of an inch deep, extending longitudinally of the driving face forming surfaces 162 to form small ribs on the driving faces of the recess. The grooves may be of constant section, as shown, or tapered (Figs 60, 61, not shown), or may be formed in the intermediate walls (184) of the punch (Figs 62, 63, not shown). Two or more grooves may be provided in each surface, and a groove or grooves may be formed in the back-out face forming surfaces 164.